In general, in the descriptions that follow, we will italicize the first occurrence of each special term of art that should be familiar to those skilled in the art of integrated circuits (“ICs”) and systems. In addition, when we first introduce a term that we believe to be new or that we will use in a context that we believe to be new, we will bold the term and provide the definition that we intend to apply to that term. In addition, throughout this description, we will sometimes use the terms assert and negate when referring to the rendering of a signal, signal flag, status bit, or similar apparatus into its logically true or logically false state, respectively, and the term toggle to indicate the logical inversion of a signal from one logical state to the other. Alternatively, we may refer to the mutually exclusive boolean states as logic_0 and logic_1. Of course, as is well known, consistent system operation can be obtained by reversing the logic sense of all such signals, such that signals described herein as logically true become logically false and vice versa. Furthermore, it is of no relevance in such systems which specific voltage levels are selected to represent each of the logic states.
Generally, the high power consumption of current integrated circuit technology has become a critical problem for mobile electronics that must run for days, months, or even years on a single battery charge. As is known, a reference voltage generator is a key element in the overall design of integrated circuits. Such a reference voltage generator is typically used to provide a stable reference voltage to the analog modules of the integrated circuit.
Shown in FIG. 1 is a typical integrated system 10 comprising, inter alia, reference voltage (“VREF”) generator 12, reference current (“IREF”) generator 14, several digital modules, and several analog modules. An example of an analog module is analog to digital converter (“ADC”) 16. Reference voltage generator 12 and reference current generator 14 are each common modules for supplying a stable reference to such analog modules. Reference voltage generator 12 is sometimes used to derive the output reference current provided by reference current generator 14. Also, reference voltage generator 12 and reference current generator 14 may be used to supply a stable reference to modules throughout integrated system 10.
Shown in FIG. 2 are three typical reference voltage generator configurations, 12A, 12B, and 12C, as discussed both in our Parent Provisional and in the Related Application. For such configurations, post-silicon trimming circuitry (“trimmer”, not shown) is typically required to adjust for operational variations and fluctuations of MOSFET M1 and MOSFET M2, and subsequently, the absolute value of reference voltage (“VREF”). As is known, the electrical characteristics of M1 and M2 are strongly influenced, at a minimum, by manufacturing variations and temperature variations. For the configurations illustrated in FIG. 2, the trimmer may not be adequate to compensate for such variations as desired.
As is known, semiconductor IC designs are generally sensitive, during normal operation, to variations in process, voltage and temperature (“PVT”). Such variations are expected, though not desired, and are a natural product of semiconductor manufacturing. During an IC design phase, conventional computer-aided design (“CAD”), computer-aided engineering (“CAE”), and computer-aided manufacturing (“CAM”) software programs enable an IC development team to design an IC while also helping to predict circuit variations and circuit sensitivities. However, if the development team and associated software programs fail to predict all sensitivities, the manufacturing process will fabricate a certain number of ICs that do not meet data sheet specifications. Off-chip test equipment will generally determine such sensitivities, but the development team must subsequently spend valuable time to debug and modify the IC. As is known, when the manufacturing process fabricates ICs below a predicted yield the result is lost revenue opportunity.
Due to sub-micron feature sizes, in addition to strict power consumption and operation requirements, reference voltage generator designs may be especially susceptible to PVT. As explained in, for example, the text book of David A. Johns and Ken Martin, entitled “Analog Integrated Circuit Design”, Wiley, pg. 360, 1997, a copy of which is submitted herewith and incorporated herein in its entirety by reference, and as illustrated in FIG. 2, certain circuits, such as bandgap reference voltage generator 12D, and the like, are known to provide a more stable reference voltage across PVT; however such circuits consume significantly more power than other reference voltage generators. Some voltage reference generators, such as reference voltage generators 12A, 12B, and 12C illustrated in FIG. 2, consume much less power; however such voltage reference generators have significantly more sensitivity to PVT than bandgap voltage references and the like.
As discussed in our Parent Provisional, we submit what is needed is an improved method and apparatus for a reference voltage generator that provides optimized power consumption, resulting in extended battery life, reduced battery size, and reduced cost. In particular, we submit such a method and apparatus for a reference voltage generator should provide an improved solution for low power supply requirements, while also providing an improved topology for trimming out PVT sensitivities. Also, the characteristics of the reference voltage generator should be controllable and observable in a manufacturing and system test environment.